This invention relates to inorganic compositions and antifriction elements produced therefrom.
Antifriction materials for use at an elevated temperature are well known, for example, as bearing materials. Suitable are carbon, graphite, glass, ceramics, and porcelain, as well as specific composite elements, such as flame-sprayed coatings of metals, alloys, oxides, or fluorides on a metallic substrate. Antifriction proerties as well as the wearability of these materials are varied. Whereas temperature resistance to decomposition is satisfactory at relatively high temperatures, excessive brittleness and very high thermal expansions make these materials highly susceptible to breakage when stressed by temperature fluctuations. Likewise, composite elements on a metallic base tend to warp.
German Pat. No. 1,300,460 describes compact layers of nickel oxide with additives of fluorides, phosphates, and several specific oxides on a substrate. In this case, the ground components, for example 90% nickel oxide and 10% calcium fluoride, are sintered and after several grinding steps, are applied by flame-spraying to a nickel-chromium alloy. It is also possible to sinter these components onto a support. The additional oxides serve to lower the melting temperatures by the formation of an eutectic.
A disadvantage of this process is the required necessary adaptation of the thermal expansion of the antifriction compound to that of the substrate. As a consequence, layers of a thickness of only 1-2 mm. can, for example, be applied by flame-spraying to the substrate, since these layers develop fine cracks due to differences in the thermal expansions. Another disadvantage is that the rustproof alloys of the substrate which, in principle, all have high coefficients of thermal expansion, tend to warp when used in an elevated temperature range, due to unavoidable temperature gradients, and this, in turn, damages the sprayed-on or sintered-on antifriction compound layer.
Further pertinent teachings relating to the production of antifriction elements based on NiO are found in British Pats. Nos. 871,293; 993,474; and 986,709.